Buildup of Gas Behind Explosion At Pemex

By

Anthony Harrup and

Laurence Iliff

Feb. 4, 2013 11:52 p.m. ET

MEXICO CITY—The blast that ripped through an office block at the headquarters of Mexican state oil monopoly Petróleos Mexicanos and killed at least 37 people was caused by an accumulation of gas, possibly methane, according to the preliminary results of the investigation, Mexican Attorney General Jesús Murillo said Monday.

Speaking at a televised news conference, Mr. Murillo said there were no signs that last Thursday's explosion,...